You can generate an FFT (fast-Fourier-transform) plot by periodically collecting a large number of conversion samples from the output of an ADC. Typically, ADC ...

Oscilloscopes are time-domain instruments, but because they digitize waveforms, oscilloscopes can process time-domain signals into the frequency domain. The FFT (Fast Fourier Transform), spectrum ...

Closed-loop control systems are sometimes shipped from the factory with resonances and other operational difficulties that aren't supposed to be part of the package and are not well understood.